Popular Science Monthly 



315 



TRANS- 

 MITTER 



jj ] [Jtransf 



^CONDENSER 

 TELEPHONE 



TRANSFORMER 



America's New Semi- 

 Wireless System for 

 Telephoning from 

 Captive Balloons 



WHAT will be still another addition 

 to the long list of America's contribu- 

 tions to the technique of modern warfare 

 is a Mtt'raZ-wireless system for communi- 

 cating from balloons. The gun-fire of 

 artillery is directed, as everybody knows, 

 by battery commanders who ascend to 

 high altitudes in anchored balloons. From 

 here the commanders take their observa- 

 tions and telephone their orders down to 

 their batteries which may be concealed 

 several miles away. To provide suitable 

 telephone transmission lines, the Allies 

 have been using the wire cables which 

 anchor the balloons. They have built 

 these cables up with an internal steel core 

 which they insulate from the outer 

 strands. But in providing two insulated 

 conductors in this way, they were com- 

 pelled to use a bulky, very expensive cable 

 which was likely to be rendered, worse 

 than useless if too roughly handled. For 

 if once this cable should become injured 

 and the two conductors become short-cir- 

 cuited, the telephones could not work and 

 the commander would be cut off from 

 his men. 



The semi-wireless system which has 

 just been brought out by William Dubi- 

 lier and Robert Goll, two American 

 engineers, does away with any need for 

 the internal core. Their system, which is 

 fully protected by patents, is expected 

 to be officially adopted by our Govern- 

 ment. For connecting paths between 

 the balloon and the ground, the new 

 system uses an ordinary solid steel cable 

 as one path, and the air itself as the 



^TRANSFORMER 



other. It therefore uses one transmission 

 line, as in wire telephony, and it also uses 

 the air as in wireless. 



Considering the diagram of con- 

 nections it will be seen that the 

 system has one secondary circuit 

 consisting of the secondaries of the 

 two telephone transformers, of the 

 two telephone receivers and their 

 shunt condensers, and of the two 

 metal sheets which, with the air be- 

 tween as their dielectric, form a balanc- 

 ing capacity. This one secondary has 

 two primaries : the telephone transmitter, 

 batteries and the primary of the trans- 

 former, in the basket, and the similar 

 instruments down below at the gun 

 battery. The three circuits are mutually 

 tuned to provide a maximum of current 

 in the secondary. 



When the commander talks into his 

 transmitter, the corresponding primary 

 current is modulated accordingly. The 

 variations in the primary currents are 

 induced into the secondary through the 

 step-up transformer. Here the variations 

 become very marked, due to the strength- 

 ening effect afforded by the' inductance 

 of the transformers and the capacity of 

 the air-condenser, which together natur- 

 ally tend to cause the secondary current 

 to oscillate. These variations are changed 

 into sound waves by the telephone re- 

 ceivers — and the gun captain thus re- 

 ceives his orders. 



A Polarity-Changer for Reversing 

 Lighting Battery Current 



SOME audion detectors work better if 

 the current from the lighting battery 

 is reversed. To do this quickly a polarity- 

 changer is very bandy. There are many 

 kinds of polarity-changers, but the one 

 here described is very compact and looks 

 neat. To make it, mount five contact 

 points on a fiber-base as shown in the 

 drawing on the following page; space 

 them about half their diameter apart. 

 The positive side of the battery is 

 connected with No. I and 5; the 

 negative with No. 3, while No. 2 

 an^l 4 are connected with the fila- 



METAL SHEET 

 BALANCING CAPACITY 



